1. Field of the Invention
This invention relates to aqueous dispersions of positively charged polytetraflurorethylene and a method for their preparation.
2. Description of the Prior Art
According to known techniques, dispersions of polytetrafluoroethylene are prepared, for example, by polymerizing gaseous tetrafluoroethylene by contact with an aqueous phase containing a polymerization initiator, an emulsifier, and if desired a buffering agent. The resulting polymer is a dispersion of fine particles protected by an emulsifier and generally possesses dimensions less than 0.5 microns.
The course of polymerization of tetraflurorethylene is greatly affected by the presence of organic compounds containing hydrogen and the only useful emulsifiers which are known today are the perfluorocarboxylic or perfluorosulphonic acids, the .omega.-hydrogenated or chlorofluorinated acids and their alkaline or ammonium salts. Since these compounds are anionic emulsifiers, the dispersions of polytetrafluoroethylene obtained are then often stabilized with a nonionic surface active agent.
Dispersions of various positively charged polymers have been prepared using cationic emulsifiers in the polymerization process. But as stated above, polymerization of tetrafluoroethylene requires the use of emulisifiers all of which are negatively charged and to this day, no cationic emulsifiers are known which would permit one to obtain dispersions of positively charged polytetrafluoroethylene.